Hi guys,

I have some questions about running 12ax7 preamp tube heaters on DC.

The filaments are pins 4,9ct, 5.

Typically they are run at 6.3 VAC in parallel ..pins 4&5 connected to one leg of Ac and pin 9(center tap of the filament) to the other leg of ac. In parallel the current draw is 300ma.

I'd like to run multiple tubes on regulated 12.6 DC. The filaments will be run in series, pin 9 not used. In series the current draw is 150ma.

How do you wire this? Put 12.6 DC on pin 5s and wire pin 4s to ground? Is it that easy? Or what am I missing?

Thanks!

 

It is just that easy. Leave pin 9 open. When running multiple tubes, they will be wired in parallel with the first tube.

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Mike ML.

 

Vacuum tubes??
Welcome to the distortion of 1950.

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Uncle $crooge

 

Or the Marshalls of the 1970's!

'Cmon Audioguru... don't you like the sound of smooth tube amps over solid state?

 

I suspect he likes quality - low distortion and good frequency response.

'Smooth' isn't an audio term, but means low quality, poor frequency response and high distortion.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

In 1950, solid state amplifiers had crossover distortion and no high frequencies. Then tube amplifiers sounded distorted but better.

How times have changed today.
Now solid state amplifiers have distortion so low that it is difficult to measure and their frequency response is a straight line from DC to green light.

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Uncle $crooge

 

And they are great for playing CDs but they sound really crap playing an instrument through.

Use A when A is best, use B when B is best, and be smart enough to know which is best and when.

 

And that amplifier was hard to make in 1950, because the transistor was not developed until 1954!

I think some people confuse the "smooth" characteristic of tubes with the pleasing sound of even order harmonic distortion, the kind you get with a class A amplifier where the top half of the waveform is compressed. I adds a nice "chorus" effect to the sound.

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-=VA7KOR=- My Solar System Includes Pluto.

 

I like what RB said... "Use A when A is best"

As a guitar player for almost 20 years, I've had several of both and it really just depends on what genre you want to sound like. Both have their pros & cons. But hey, if it sounds good...

 

They make the instrument sound as it's supposed to, a valve amplifier colours the sound to make it different (limited frequency response and high distortion).

If you want such a coloured sound a valve amp is the best way to go.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Sure they affect the sound, but with modern instruments (say electric guitar) the amp is very much a PART of the instrument.

As an example you could say the spruce top of a classic violin gives it a "smooth" sound by attenuating the high frequencies. You could make the violin top out of high tensile steel and it would have "much better high frequency response" but then it would sound tinny, harsh etc. Having an instrument where all the frequencies are reproduced equally is NOT a guarantee it will sound better.

 

Tube amps generate frequencies (due to harmonic distortion) that are not present in the input. This is different from modifying the frequency response. I'm not saying this is necessarily bad, but it is different from your example.

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Ron

 

You don't need to use a vacuum tube amplifier to rolloff the high frequencies. A tone control circuit will do the same but will not add distortion like vacuum tubes unless the tone control circuit also has vacuum tubes.

__________________
Uncle $crooge

 

Question: How many engineers does it take to answer a question about series-parallel connections?

Answer: ONE to answer the question; and FIVE to argue about deep-seated personal preferences!

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Mike ML.

 

Dude... this is more than a preference... it's a Jihad!